Today’s door closers are much improved versions of old technology. A main spring inside the closer body wants to slam the door shut quickly but is prevented from doing so by the restricted flow of hydraulic fluid through a series of valves.
Controlling the speed of hydraulic fluid controls the speed at which the door closes. The above image uses three needle valves (shown in grey) to control door closing speed.
One valve controls the majority of the closing cycle called swing speed.
Another valve works in the opposite and provides a cushion against the door being flung open too fast. This is called the back check feature protects the door and its hardware.
The third valve controls latching speed which many times needs to be a bit faster than the swing speed. It needs to overcome changes in air pressure, the force required to retract the latch into the door lock, and compensate for any misalignment of the door.
Each valve has its own separate function and can be adjusted as needed. One note of caution, however. Don’t back out the valve adjusting screw too far or it will fall out on the floor, along with about a quart of closer fluid that is lots of fun to clean up.
Replacing A Closer
To replace a door closer first begin by looking for a model number on the closer body. This will typically by shown as a sticker placed somewhere on the body.
A common mistake is to find a casting number formed into the body and believe it is a model number. Castings are used for many models and sometimes even used by different manufacturers. Look for a sticker, not a casting number.
If no label can be found the next best thing is to measure the bolt hole pattern. Knowing the pattern will narrow it down to a model or two and your hardware specialist can pinpoint the exact model for you. It’s always a good idea to reuse existing bolt holes when replacing a closer because drilling and tapping new holes is no treat.